One more vital requirement should always be kept in mind: A battery manufacturer who buys cells for their production from a reliable source, and receives UN38.3 test reports for these cells, must once more subject the whole battery pack he has built to the full testing procedure.
This is to detect any design or construction flaws, and check if, in the process of connecting the cells into a battery, none of the cells has been damaged.
Mechanical damage, short circuit or overheating of one cell causes a chain reaction. A battery fire is almost impossible to control without specialized extinguishing agents.